1. Field of the Invention
The present invention relates to a method for controlling the sub-scanning of a document reading machine wherein an original document is resolved into picture elements and read to provide a print on the basis of the read picture information.
2. Description of the Prior Art
A digital copying machine of the type in which an original document is resolved into picture elements and read to provide a print on the basis of a picture signal obtained from the reading of the elements, has two functions of reading the document to generate the picture signal and providing a print on the basis of the picture signal. Accordingly, it is considered that such a copying machine can be applied as a composite machine having a combined function of a facsimile and a printer.
In the event where the above digital copying machine is arranged as such a composite machine, however, it requires predetermined data processings including code conversion and thus a waiting time at the time of input and output of the picture information, resulting in that the reading and printing operations of the document must inevitably be effected at a variable speed.
In such a case, since the reading section forms a secondary vibration system having a mass, vibration occurs in the movement of the reading section during switching from one speed to another and this vibration causes the irregularity in the sub-scanning feed of the reading section, whereby the picture quality is deteriorated. FIG. 1 shows a secondary vibration system, in a model form, of the reading section, wherein M is a mass, K is a spring and C is a damper. FIGS. 2(a) and (b) are graphs showing to the reading section with respect to time and shift of the reading section shift with respect to time, showing how vibration occurs when the command speed to the reading section forming such a secondary vibration system abruptly changes from V.sub.1 to V.sub.2. It will be seen from FIGS. 2(a) and (b) that, when the command speed to the reading section abruptly changes from V.sub.1 to V.sub.2, the shift X of the reading section with time "t" is as shown in FIG. 2(b), that is, an undesirable vibration takes place in the reading section.
In view of the above circumstances, it is an object of the present invention to provide a method for controlling the sub-scanning of a document reading apparatus which does not cause any vibration in the reading section even during its switching of the speed, whereby the stable feed of a reading section can be achieved.